The present invention relates to a flight control system for controlling a flight of an aircraft. More particularly, the present invention is concerned with a flight control system including a manual control member and a power-assist actuator for controlling a control surface on the basis of an operation force exerted on the manual control member and a force mechanically fed back to the manual control member from the control surface.
Conventionally, there have been provided a flight control system shown in FIG. 5 as comprising a manual control stick 1, a pivotal support member 2 forming part of the aircraft, a control surface 3, and a transmission linkage 4 provided between the manual control stick 1 and the control surface 3. The manual control stick 1 has a manual input portion 1a, a pivot portion 1b and a control force output portion 1c connected with one another. The manual input portion 1a of the manual control stick 1 is manually operated to have the control force output portion 1c pivotally move around the pivot portion 1b. The control surface 3 has a surface pivot portion 3a and is pivotally mounted at the surface pivot portion 3a on a support portion, not shown, forming part of the aircraft. This control surface 3 is controllable to assume different angle positions within a predetermined control angle range, and is controlled by the control force outputted from the manual control stick 1. The transmission linkage 4 is constituted by a link member 6, a first pulley 7 having a rotation shaft portion 7a rotatably supported by the body of the aircraft, a second pulley 8 having a rotation shaft portion 8a rotatably supported by the body of the aircraft and connected to the surface pivot portion 3a of the control surface 3, and an endless belt 9 put round and encircling the first and second pulleys 7 and 8. The transmission linkage 4 is adapted to transmit the control force from the manual control stick 1 to the control surface 3 and the reaction force mechanically fed back from the control surface 3 to the manual control stick 1.
The flight control system of this kind is simply structured as above, and therefore utilized widely for aircraft of small sizes. In the case that the control surface is equipped with a balance tab, a spring tab or the like which is designed to assist the manual operation force of the control member by the air force exerted on the tab or the like, the above flight control system can be utilized for aircraft of part of middle sizes.
The above flight control system, however, cannot be utilized for aircraft of large sizes and most of middle sizes because the reaction force beyond the human power is mechanically fed back from the control surface to the manual control stick if the above flight control system were utilized for such aircraft.
To avoid these inconveniences, it has been proposed various powered flight control systems each adapted to perform an irreversible control and having a control actuator for controlling the control surface with the force beyond the human power.
Each of the flight control system, however, needs a plurality of actuators each operable to control the control surface and able to substitute for another, since one of the actuators may fail in spite of the fact that the control surface cannot be controlled by the human power. Each of the flight control systems is further required to comprise control means such as for example an SAS (Stability Augmentation System), a CAS (Control Augmentation System), a FBW (Fly-By-Wire) system or another large-scale servo control system.
This results in the drawback that the above powered flight control systems are costly and therefore insufficient to be utilized for aircraft of small and middle sizes.
The present invention contemplates provision of an improved flight control system overcoming the above inconveniences of the prior-art flight control systems.